The present invention concerns automobile road vehicles, with series hybrid motorization. In vehicles of this type an engine drives an electric alternator which transforms the mechanical energy delivered by the output shaft of the engine into electrical energy. This electrical energy powers one or more electric traction motors, which are mechanically connected to the drive wheels of the vehicle. The engine is not mechanically connected to the wheels, in contrast to vehicles with parallel hybrid motorization, in which a engine and an electric motor are both connected mechanically to the drive wheels so that the torques they deliver can act additively to drive the drive wheels.
Drivers of classically motorized automobile vehicles (“classically motorized” is understood here to mean a engine and a mechanical or automatic gearbox) are familiar with the acceleration and braking controls well known in the state of the art. These controls have attained a high degree of progressiveness and reactivity. It is desirable for a hybrid vehicle to be able to be driven in essentially the same way if one wishes not to confuse a driver used to the classical motorizations. This entails transforming the driver's actions on the accelerator pedal (and if necessary the brake) into appropriate actions on the traction chain that begins at the and ends at one or more electric traction motors.
It is well known to fit a battery of electric accumulators as a buffer between the alternator and the electric motor, particularly in the case when it is desired to be able to drive the vehicle in the purely electric mode, with the engine cut off. In that case the controls of the engine and the electric traction motor can be independent. There is no particular problem in controlling the torque of an electric motor which draws its energy from a battery of electric accumulators, with all the progressiveness and reactivity desired at the accelerator pedal available for the driver's use.
But the use of a battery of electric accumulators raises different problems. Such a battery is heavy in relation to the quantity of electrical energy stored. This considerably increases the mass of a vehicle and is a source of waste during accelerations, not to speak of problems related to the dynamic behavior of a vehicle, which are the more crucial the heavier the vehicle is. In addition, such batteries pose maintenance problems and problems for the environment because of the many materials they contain which are polluting and difficult to recycle.
The purpose of the present invention is thus to design a series hybrid traction chain that can if necessary operate without a battery of electric accumulators, while providing the driver of the vehicle with a very progressive and very reactive accelerator control. In the case when no reservoir of electrical energy (battery) is available, it is necessary to be able to produce just that electrical energy which is required for the demand. The problem arising is therefore to obtain the desired torque from the electric traction motor while avoiding stalling or racing of the engine, and this by means of a control system whose progressiveness and reactivity are as close as possible to those of the accelerator pedal of a classically motorized vehicle.
Patent application EP 1 241 043 describes a traction chain for a series hybrid vehicle in which the driver's demand, when he presses the accelerator pedal, results in a command to open a throttle valve for the engine. The speed of the engine is a consequence of controlling the torque of the electric traction motor(s), an operational mode on which the principle proposed earlier has no direct action. The torque of the traction motors is controlled as a function of the vehicle's speed and as a function of a controlling power P which evaluates the power available at the drive output shaft of the engine at the engine's real speed. The operating mode of the engine does not necessarily correspond to optimum consumption, despite a tendency described in the aforesaid patent application to evolve progressively towards operating modes with lower consumption.
To move rapidly and in a more deterministic way towards optimum operation of a given engine, in particular towards optimum consumption by a given engine, it would be necessary for any driver command to be able to control both a given throttle valve opening and a revolution speed of the engine in question.